Insulating bushings and interconnection box cable connecting fittings are well known in the prior art, as illustrated by U.S. Pat. Nos. 2,948,973 to Hawes; 3,424,856 to Coldren; 3,991,446 to Mooney et al; 4,262,409 to Madej; 4,299,363 to Datschefski; 4,350,839 to Lass; 4,366,343 to Slater; 4,474,489 to Simon; and particularly 3,493,205 to Bromberg. The Hawes, Coldren, Mooney et al, Datschefski, Simon, and Bromberg patents are all directed to fittings for installing and securing single sheathed cables to an electrical panel. The sheathed cables may each include multiple conductors and typically may include an outer plastic protective shield. None of these prior art fittings are specifically designed for safely securing two or more cables, such as nonmetallic sheathed cables, to the panel. None provide a plurality of generally rectangular channels, each for housing one or more cables. Among these prior art patents, the Slater 4,366,343; the Madej 4,262,409; and the Lass 4,350,839 patents disclose devices with structure that permits relatively unrestricted cable entry, but positively inhibits cable withdrawal. Of these, the Slater 4,366,343 device is an integral portion of the panel (and is thus difficult and expensive to mold). The Lass device requires non-standard rectilinear holes in the enclosure, and the Madej device is an essentially 3-piece molding having a split base portion; the latter is both difficult and expensive to mold, and is structurally weak around the periphery of its split base portion.
Also, U.S. Pat. Nos. 4,000,875 to Jemison et al and 4,190,222 to Appleton et al, and British Patent No. 1,122,395 to Griffiths include primitive features which are improved upon by the present invention. The Appleton et al and Jemison et al patents both disclose fittings or bushings which utilize a cammed head to clamp a single cable within the bushing. The cam head of Appleton et al is rotatably mounted in the bushing with a pair of radially extending transverse axle shafts, forming a two-piece construction, while Jemison et al relies on a flexible hinge of the same material as that of the bushing. Additionally, Jemison et al incorporates a toothed surface on the cable engaging cam head surface, while Appleton et does not include such a feature. Both teach the use of a single cam head. Both are positively forced into gripping relationship with the cable; neither permits a straight-through cable design, as both deflect the cable from its normal path in order to position it relative the cam head and another member for engagement. The Griffiths design is intended for mounting in a square hole, though current wiring practices are directed to round holes; while it may be adaptable for anti-withdrawal of a cable therein, the fitting and connector are to be inserted in the mounting hole together rather than permitting independent insertion.
The Appleton et al and Jemison et al fittings are believed to be incapable of meeting the present Underwriters' Laboratories standards which requires gripping of the cable sheath without tearing it when the cable is subjected to certain tension forces, and without tearing apart of the fitting.
Great quantities of such cable fittings are required in wiring commercial and residential structures; thus they must be safe, durable, and inexpensive, and they should be easily installed without special tools or without involving additional labor. Multiple piece fittings are typically more expensive to mold than single piece fittings and are also typically more difficult and cumbersome to install, thus adding to their installed cost. It is preferred that cable fittings easily accept insertion of the cable while severely restricting cable withdrawal; safety standards entities such as Underwriters' Laboratories often require that such fittings meet stringent anti-withdrawal standards and may also require easy insertion of the cable. Further, the strength and integrity of the cable fitting is believed to be greatly enhanced when at least one end portion is circumferentially uninterrupted, especially the end portion which is snugly fitted to the panel.
Thus, there exists a need in the art for a one-piece, economically molded cable fitting which provides safe, non-destructive one-way restraint of the cable at the panel, includes an uninterrupted end portion of the fitting adjacent the panel for strength, and is capable of passing present safety standards.